This week the Simons Center is hosting a workshop on “The Geometry and Physics of Scattering Amplitudes”, talks are available here. Last week they (and the YITP) held a one-day symposium on Trees, loops and precision QCD, based around the work of Zvi Bern, Lance Dixon and David Kosower that was recently awarded the 2014 Sakurai Prize. For more about this, see Dixon’s guest post here, or his talk at the symposium.
Bern, Dixon and Kosower started working on amplitudes more than twenty years ago, at a time that it was becoming clear that string theory was not working out as a theory of everything. Calculations in string theory did though lead to interesting new ideas about how to evaluate scattering amplitudes in gauge theory (I see from Dixon’s list of publications that in 1994 he wrote something for the SLAC Beam Line on “Whatever happened to the theory of everything?”, presumably about this, but now too deep in the past to be available on-line). The three Sakurai Prize winners have been steadily working at the problems of amplitudes in gauge theory and quantum gravity, for many years without getting much attention for their work. About ten years ago, things changed when Witten wrote a paper about getting amplitudes from the “twistor string”, a topological string theory in twistor space (the use of twistor space was originated by Penrose back in the late 1960s, and was applied by V.P. Nair to gauge theory amplitudes back in 1988 while he was here at Columbia).
About six years ago Nima Arkani-Hamed entered the subject, where he has had a dramatic effect as an impresario, arguing that this is a route to revolutionary ideas about physics, overthrowing conventional notions of space and time, locality and unitarity, and doing away with the notion that gauge invariance is important. This was partly responsible for his $3 million Milner prize.
For the latest along these lines, a paper with Trnka about “The Amplituhedron” has just appeared, a topic which got wide play in the press earlier this year as Physicists Discover Geometry Underlying Particle Physics, drawing a parody from Scott Aaronson about his own work on the “Unitarihedron” and “Diaperhedron”. Arkani-Hamed’s talk at the Symposium covers both the ideas of Bern, Dixon and Kosower and his recent work with Trnka. It includes many appreciative remarks about their work, including some interesting commentary on how theoretical physics is done. For instance, on the likely reason for people ignoring their early work:
It’s a natural reaction among theoretical physicists, right? At any given time there’s all sorts of interesting things going on, things that other people are doing and things that you are doing and especially if someone else is coming along with something that looks really exciting, in order to justify not dropping everything you have and working on it you have to sort of start inventing these reasons why what they are doing is irrelevant or crap, right? It’s a very human thing, a very human thing, a very natural thing. I think everyone does it to some extent, and really good people eventually will realize that they are fooling themselves and start changing their tune if it’s appropriate. Really bad people, well, we won’t talk about them. It was not at all obvious that this was the tip of a huge iceberg…
Often fields, other fields, have what you might call prophets and there’s I think usually an excessive amount of reverence for these prophets, because the prophets tend to have the property that they say some sort of vague things, I won’t name any names but you can probably figure out the sort of collection of people I’m talking about. They say some sort of vague things about what might happen with physics in the future, and then twenty years later when other people have done all the hard work and really figured out what is going on and how it works in detail and why it works that way and not another way, if it vaguely looks like something they did, they say “see, I said so all along!” They have a fair amount of attraction, I think it’s because a lot of physicists have father-figure issues. But anyway, Zvi and Lance and David were very much not like that, they weren’t just vague prophets saying something was going on, they were extremely specific: there was something going on in this area with these kind of computations in this arena and they knew it. And it took a decade or more for many other people in the field to catch up.
(Personally, I have no idea which “prophets” he’s thinking of.)
Finally, there were some personal comments contrasting Bern, Dixon and Kosower’s low-key style and use of a variety of techniques with his own high-powered hype-driven sales-job of specific ideas to himself and others. Probably a good idea to read this in conjunction with the “Outlook” section of the new paper….
I must say, and I’m really not just saying this to say it, I’m VERY envious of this, because I AM an ideologue. In my defense at least I can say that I’m a serial ideologue, in the sense that I’ll take totally different ideologies and drop the last one without thinking about it, but it’s very important for me personally to be an ideologue when I’m working on something and I think, and I’m saying this in all honesty, the difference is talent. If you’re really good, you don’t have to be an ideologue. You take this, you take that, you’re solving for things left and right, you don’t care where things come from. If you’re not as good, there are 15 million things going on, you’re holding on for dear life in the stiff wind of all the crazy stuff going on in the subject. So you have to have a strong point of view about something, you have to have a strong point of view to sort of pursue a particular direction, otherwise you’ll get beaten around all the time and get nowhere.
So, usually I’ll get up when I talk about scattering amplitudes and give a long introduction about how spacetime is doomed, we have to find some way of thinking about quantum field theory without local evolution in space time and maybe even without a Hilbert space and blah-blah-blah. This is all very high-falutin stuff, this is stuff that Lance wouldn’t be get caught dead saying. I think none of these guys would ever say something that sounds so pretentious, but I have to say it, you know I have to say it, because this is the only way I can get up in the morning, and like “I suck again, OK, here we go, I’m doing it because spacetime is doomed, I swear to God, right”. But, quite seriously, the best people in the subject have this feature, they don’t need to be ideologues, they take the most interesting ideas from every direction they can to make progress, so I really am quite envious.